text: Henri Becquerel, while experimenting with fluorescence, accidentally found out that uranium exposed a photographic plate, wrapped with black paper, with some unknown radiation that could not be turned off like X-rays.
  Ernest Rutherford continued these experiments and discovered two different kinds of radiation:
  * alpha particles that did not show up on the Becquerel plates because they were easily absorbed by the black wrapping paper
  * beta particles which are 100 times more penetrating than alpha particles.
  He published his results in 1899.
  In 1900, Becquerel measured the mass-to-charge ratio () for beta particles by the method of J. J. Thomson used to study cathode rays and identify the electron. He found that  for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron.